Adjustable circuit control apparatus



Nov. 20, 1956 FLUBACKER 2,771,570

ADJUSTABLE CIRCUIT CONTROL APPARATUS Filed April 5, 1952 VoLTA 65 CURRENT IN V EN TOR.

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United States Patent ADJUSTABLE CIRCUIT CONTROL APPARATUS Charles H. Flubacker, Chicago, 111., assignor to Cook Electric Company, Chicago, Ill., a corporation of Illinois Application April 5, 1952, Serial No. 280,825

1 Claim. c1. 317 139) This invention relates to circuit control apparatus and more particularly to circuit control apparatus having provisions for the independent adjustment of the voltages at which the apparatus will be actuated and deactuated.

It is a principal object of this invention to provide improved apparatus for controlling external circuits in response to predetermined applied voltages.

While various apparatus has heretofore been proposed for the control of the operation of circuit control apparatus and to adjust its operating points, it is an object of this invention to provide improved apparatus which will be capable of more accurate control of the actuated and deactuated voltages independently and over wide ranges.

It is a further object of this invention to provide improved circuit controlled apparatus which will be positive in operation, eliminating erratic operation and chatter, especially where it is desired that the voltages for actuation and deactuation be substantially the same.

It is another object of this invention to provide improved apparatus for circuit control which will be adjustable over an extended range of applied voltages.

Further and additional objects and advantages of this invention will be apparent from the description, accompanying drawing, and appended claim.

In carrying out this invention in one form, apparatus is provided which includes a relay coil having an associated switch therewith adapted to control various external circuits. The current in said coil is controlled by two series connected adjustable resistors, one of which is in circuit at all times and thus determines the applied voltage at which said coil will be sufficiently energized to actuate the associated switch mechanism.

The second series resistance is inserted into the circuit only when the relay coil is energized and the associated switch mechanism actuated. Thus, when the switch is actuated, the second series resistance is inserted in the circuit and reduces the current for a given applied voltage. The adjustment of the magnitude of this resistor will therefore determine the applied voltage at which the coil will be de-energized and the associated switch deactuated.

Additionally, this invention provides means to reduce erratic operation of this control function by delaying the insertion of the second series resistance.

For a more complete understanding of this invention reference should now be made to the accompanying drawing, wherein Figure 1 is a graphical representation of the currentvoltage relationship of apparatus incorporating the teaching of this invention; and

Fig. 2 is a schematic circuit diagram of one embodiment of this invention.

Relays and other electromagnetic devices have certain innate characteristics which are often undesirable but cannot be eliminated. One such characteristic well known in the art is the fact that the current required to actuate a relay greatly exceeds the current which will allow the relay to drop out or deactuate. This results from the retentivity of the magnetic portions of the device and from the improved magnetic flux path which results from the drawing up of the armature of such a relay. This I ratio of pick-up current to drop-out current is often of the order of two to one. In view of this characteristic, the use of relays for control purposes, where the relay current is generated by a sensing element, will result in operation over a broad range with consequent continuous hunting of the controlled function. This hunting can be substantially eliminated by the teaching of this invention.

Referring now to the drawing and more particularly to Fig. l, the theory of operation of this invention will be apparent from the curves herein represented. In Fig. 1, the solid line 12 represents the current in the actuating coil for the switch mechanism of this invention and will correspond to various applied voltages represented by curve 13. The voltage of curve 13 may represent the output of any device whose operation it is desired to control. This could be a D. C. source, such as a thermocouple voltage or bridge output, or an A. C. source, such as the output of a generator or voltage regulator.

While, herein, one particular curve has been chosen to represent and illustrate the various operating voltages and voltage-current relationships, the apparatus with which this control device is utilized will determine the actual shape of the curves. The principles applied to each case will be identical and no departure from the teaching herein would be required irrespective of the particular apparatus or the type of voltage which is supplied.

In the curve 11 the voltage is shown as a constantly increasing function with respect to time, and as the apparatus of this invention is a substantially linear impedance, the current represented by curve 12 is also a constantly increasing function with respect to time.

At point 14 on the voltage curve the corresponding current is represented by point 15 on the solid curve 12. Point 15 represents a current which is on dotted line 18 and of sufiicient magnitude to cause actuation of the switch mechanism and application of power to the external loads. At this point a series resistance is inserted in series circuit with the coil of this apparatus and will cause a current reduction to the point 16 on curve 12, which may be very close to the current which will cause deactuation represented by dotted line 17. Assuming that the voltage continues to rise for a short time after actuation, curve 13 is shown reaching a maximum voltage and then beginning to decrease. This would be true of thermocouple voltages or the like wherein this apparatus controls the power source, and there is a time lag before the change takes efiect. correspondingly, curve 12 reaches a maximum current and also begins to decrease. As the current decreases, the current curve 12 crosses line 17 which is the deactuating current of this device and the switch means which controls the external circuit apparatus will be deactuated.

However, it is desired that the series resistance remain in circuit for a short period of time as the immediate removal of said resistance would cause a substantial increase in current and would approach the actuating current represented by dotted line 18, and would cause erratic operation and chatter of this apparatus.

Thus, in this apparatus means is provided to effect a time delay in the removal of the series resistance such as represented by the time increment 19. At the end of the time increment, removal of the series resistance will cause the current to substantially increase, but to increase only to a value substantially below the energizing current 18. This current is represented by point 21 on the current curve 12.

The circuit diagram of Fig. 2 illustrates one apparatus 22 for accomplishing this type of operation. The voltage input is represented by terminals 23 and 24, and the actuating coil 25 has adjustable resistances 26 and 27 in series across these terminals. Coil 25 has normally closed contacts 28 and normally open contacts 29 associated therewith. Normally closed contacts 28 are in series relation with a second relay coil 31 and an appropriate voltage source such as battery 32. Normally open contacts 29 are adapted to control any external apparatus 30 upon which this device may be desired to function. Coil 31 has normally open contacts 33 adapted for actuation thereby and normally open contacts 33 are connected in parallel relation with adjustable resistor 27.

The manner in which this circuit functions is as follows: a voltage is normally applied to terminals 23 and 24 and will be applied to the circuit through contacts 33 which are now actuated by virtue of the current in coil 31 caused by the voltage source 32 in series with normally closed contacts 28. Closed contacts 33 are in series With adjustable resistor 26 and relay coil 25 and thus a current will flow from terminal 24 through normally opened contacts 33, resistor 26, coil 25 and back to terminal 23. The voltage-current relationship in the circuit will be determined by the adjustment of resistor 26. When the voltage reaches a predetermined value, controlled by the adjustment of resistor 26, a current will be established in coil 25 which is suflicient to cause actuation of the associated switch members 28 and 29. This will apply voltage to the external circuits 30 through normally open switch 29 and will de-energize coil 31 upon the opening of normally closed switch 28. This de-energization of coil 31 will cause normally open contacts 33 to be open and will thus insert adjustable resistor 27 into the control circuit of coil 25. This control circuit will now be traced from terminal 24 through adjustable resistor 27, adjustable resistor 26, coil 25 and back to terminal 23. Resistor 27 therefore can be adjusted so that a predetermined applied voltage at terminals 23 and 24 will cause a current to flow in coil 25 which will maintain sufficient energization and consequent actuation of the associated switch members 28 and 29.

Thus, by the proper adjustment of resistor 27 the dropout point of voltage represented by point 34 in Fig. 1

can be controlled over any desired range. However, it is desirable that this voltage always be chosen in such a manner that upon de-energization of coil 25 and the consequent removal of resistor 27 from the series circuit, removal of said resistor will not cause such an increase in current that the coil 25 would once again open switch member 28 and cause this mechanism to cyclically operate or oscillate.

The choice of relay 31 will determine the exact duration of the time interval 19 of graph 11 in Fig. 1. Various slow release and time delay relays may be employed to cause the precise control characteristic which is desired. A relay having an adjustable time delay may also be utilized which gives the apparatus additional versatility.

Without further elaboration, the foregoing will so fully explain the gist of my invention that others may, by applying current knowledge, readily adapt the same for use under varying conditions of service, without eliminating certain features, which may properly be said to constitute the essential items of novelty involved, which items are intended to be defined and secured to me by the following claim.

I claim:

Circuit control apparatus for controlling external circuits in accordance with the magnitude of a controlling voltage comprising electromagnetic means to be energized by said controlling voltage, contact means controlled by said electromagnetic means for completing such external circuits, first resistance means in series with said electromagnetic means to determine a first control voltage of such external circuits, normally closed contact means to be opened by said electromagnetic means at said first control voltage, second electromagnetic means including time delay means to be energized when said normally closed contact means are closed, normally open contact means to be closed by the energization of said second electromagnetic means, and second resistance means connected across said normally open contact means and in series with said first resistance means and first electromagnetic means to determine a second control voltage for such apparatus.

References Cited in the file of this patent UNITED STATES PATENTS 2,307,576 De Croce Jan. 5, 1943 

